Retriggered direct coupled sweep circuit



Sept. 15, 1959 R. F. CASEY RETRIGGERED DIRECT COPLED SWEEP CIRCUIT FiledJune 14, 1954 PLATE CURRENT ATIILZMWSO INVENTOR.

ROBERT CASEY BY' im* 9% ATTQNEYS F ig.. 2

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United States Patent O RETRIGGERED DIRECT COUPLED SWEEP CIRCUITApplication June 14, 1954, Serial No. 436,455

7 Claims. (Cl. Z50-27) This invention relates to a circuit combinationfor the production of sharp voltage pulses which can be used fortriggering purposes generally, including self-triggering.

As is well understood in the art, a triggering voltage pulse can beobtained from a point of cyclically varying potential. The difficulty isthat as the potential changes cyclically the triggering point is difcultto repeat With exact timing and wave form so that a sharp pulse whichavoids these difficulties is desirable. By the usual methods a sharpvoltage pulse is obtained by generating a compleX wave form, clippingit, integrating it and differentiating it as necessary to produce therequired sharp pulse. Very often a clamping tube or a switch tube isalso required. Obviously this method provides the desired sharp pulse ofproper characteristics but only at the expense of apparatuscomplication.

An object of this invention is to provide a very simple circuitcombinationby means of which sharp -voltage pulses are produced.

Another object of the invention is to combine the pulseforrning meanswith a switch or clamping tube.

Still another object is to produce a sharp pulse at the end of thefly-back or retrace line rather than at the start of a new cycle, thusinsuring greater accuracy in timing.

`Other and more detailed objects of the invention will be apparent fromthe following disclosure.

One embodiment of this invention is shown in the accompanying drawingsfor illustrative purposes. Thus, in Figure 1 is diagrammaticallyillustrated a circuit in accordance with this invention;

Figure 2 is a graph of important current-voltage relations in thecircuit of Figure 1;

Figure 3 is a diagrammatic illustration or chart of the associated Waveforms involved in the over-all operation of the circuit.

In Figure 1 there is illustrated at 11 a multielectrode electrondischarge tube specifically a pentode. A suitable source of cyclicallyvarying potential is diagrammatically illustrated at 7, grounded at oneterminal and connected at the other to the anode 12 of the pentode. Thissource is shunted to ground by means of a capacitor 13. The cathode isgrounded in the usual manner and is interconnected withthe suppressorgrid 9, likewise a usual arrangement. The screen grid 14 is connected tothe cathode 17 of a triode 15 to provide a cathode follower ampliiier.The control grid of the triode is provided with negative bias by meansof the grounded potential source 42. The anode of the triode isconnected through the usual resistor to ground through a suitablepotential source 40 so as to be held at the proper positive potential. Aterminal 21 is connected to the anode of the triode andpprovides anoutput connection for supplying sharp triggering pulses yfor any usefulpurpose. The control electrode 19 of the pentode 11 is connected to oneoutput terminal of a grounded source 20 generating a control voltage ofsuitable wave form such as the rectangular wave form shown. There aremanysuitable sources of `ice cyclically varying potential available forcontrolling the grid 19, including the voltage generator disclosed in mycopending application Serial No. 446,011, tiled July 27, 1954, nowabandoned. The output triggering pulse which appears at the terminal 21,among its many uses, is employed to control the generator 20 asindicated by the connection thereto as diagrammatically illustrated inFigure 1.

Referring to Figure 2, there is shown a characteristic of the usualpentode operation. As shown in this chart, as the plate voltage becomessmall, other parameters remaining constant, the plate current asindicated by the solid line decreases, while the screen grid-currentdesignated by the broken line increases sharply, their sum at all timesbeing substantially constant.

It is Well known in this art that the screen grid of a multielementelectron tube should be maintained at a lower potential than that of theanode. It this relation is reversed, that is, if the screen grid is at ahigher p tential than the plate, electrons would be attracted to thescreen grid and the resultant current would increase to the dangerpoint.

In accordance with this invention, there is provided a novel circuitwherein the sudden surge of screen grid current, instead of creating anunsafe condition, is employed to produce a controlled sharp voltagepulse suitable for triggering other circuits such as a multivibrator ora like arrangement.

In the operation of this circuit, when sweep capacitor 13 is charged bythe source 7 a high positive potential is` also applied to the anode 12.Assuming that the control grid 19 at the time t-1 is caused to becomemore positive by the application thereto of a voltage from the source20, as indicated, pentode 11 becomes conductive. As a result thecapacitor 13 is discharged and at the same time the potential on theanodeL 12 decreases rapidly. This rapid discharge represents the retraceor fly-back line of a cycle. As the plate potential drops to a lowvalue, 3the retrace will terminate and this is assumed herein to occurat the time t-2. Potential relations between the screen grid 14 and theanode 12 are now reversed. That is, the anode potential is lower thanthat of the screen grid. As previously suggested in connection withFigurey 2, the screen grid current then ysuddenly increases to a veryhigh value, impressing a pulse signal on the cathode 17 of the cathodefollower' amplifier 18. This amplified signal pulse of sharp wave formappears at the output terminal 21 for any suitable use. ln addition, asherein disclosed this pulse is applied to the voltage source 20, as forexample, the control grid of the generator, thereby triggering thatcircuit and causing the control grid 19 to go negative. This terminatesthe pulse rendering pentode 11 non-conductive whereupon capacitor 13 isrecharged by the source 10. v

These various operations are diagrammatically illustrated by the chartsin Figure 3. Sweep curve A represents the output of the generator 7. Asimple sweep function has been chosen for illustrative purposes, butthose skilled in the art will understand that more complex wave formsmay be employed, `as for example, la staircase wave form. Curve B is achart showing the wave form of the output of the 4source 20, that is, ofthe voltage pulses applied to the control grid 19. Curve C is a graph ofthe resultant screen grid current which is simply amplified by thetriode 18 and `appears at the terminal 21. At this point it may benoted, as will be understood, that the output pulse could be takendirectly from, the screen grid 14 through a resisor, but the preferredembodiment as shown in Figure l is employed because it permits thepotential of the screen grid to remain constant, thus` improving thepulsek wave form characteristics of the circuit.

Asindicated in Figure 3, the retrace begins at the y time t-l and thisoccurs also at the time that the control signal of source Z0,represented by curve B, rapidly increases to its maximum value. Thereversal of voltage relations previously referred to occurring at Vthetime t-,2 produces the sharp output pulse represented by graph C.. Thisfigure also illustrates the fact that this pulse can be used toterminate. the control signal from the source Z0, whereupon the voltageofthe sweep. curve A as indicated thereby, rises rapidly to rechargecondenser I3 to start the cycle oven again.

It will be apparent to those skilled in the art from this disclosurethat the specific embodiment -selected for illustrative purposes iscapable of variations by those skilled in the art, and I thereforeprefer to be limited by the appended claims rather than to the selectedillustrative embodiment of this disclosure.

I claim:

1. A circuit 'for producing a triggering pulse comprising: a firstelectron discharge device having at least an anode, a screen grid, acontrol grid, and a grounded cathode; a source of constant potentialhaving one end grounded; an output circuit including a second electrondischarge device having a cathode connected to said screen grid, ananode connected to the other end of said source through a load resistor,and a grid connected to 1-bias voltage to maintain said screen grid at agiven potential; grounded means applyi-ng a decreasing potential to saidanode of said first electron discharge device; a utilization circuitconnected between said control grid of said iirst electron dischargedevice and said anode of said second electron discharge device, saidtriggering pulse appearing across said load resistor and energizing saidutilization circuit when said `decreasingpotential on said anode Afallsbelow said given potential.

2. A retriggering sweep generator circuit comprising; a first normallynon-conductive electron discharge device haw'ng at least an anode, ascreen grid, a control grid, and a grounded cathode; a sweep capacitorconnected between said anode land ground; means charging said sweepcapacitor; pulsing means connected to said control grid to cause saidelectron discharge device to become alternately non-conductive orconductive to discharge said sweep capacitor during periods ofconductivity; a source of constant potential having one end connected toground; a retriggering circuit including a second electron dischargedevice having an anode connected through a load resistor to the otherend of said source, a control grid connected to a bias voltage and acathode connected to said screen grid, to maintain said screen grid at agiven potential; a connection from said second electron ldischargedevice anode to said pulsing means to terminate said period ofconductivity of said rst electron discharge device to charge ysaidcapacitor during a period of non-conductivity of said rst electrondischarge device.

V3. A circuit for producing a sharp pulse comprising: a first electrondischarge device having lat least an anode, a grid, and a groundedcathode;,a source 'of constant potential one end of which is grounded;first means connected to the other end of said source to maintain saidgrid at a predetermined potential, said first means comprising a secondelectron discharge device having at least a cathode connected to saidgrid of said first device, an anode connected to they other end of saidsource through a load resistor, and a grid connected to a bias voltage;grounded' second means applying a decreasing potential to said anode ofsaid rst device to produce a sharp pulse at said grid of said rst devicewhen said anode of said first device falls below said predeterminedpotential.

4. A circuit for producing a sharp pulse, comprising: a pentode, havingan anode, a screen grid, a cathode, and a, control grid; means to applya substantially constant potential to said screen grid, saidA meanscomprising, an electron discharge device having an anode, a controlgrid,

`and a cathode connected to said screen grid, whereby the circuitcomprising said screen grid and said cathode of said device causes saidelectron discharge device. to act as a cathode follower, a source ofsubstantially constant potential, a connection between said control gridof said electron discharge device and said source whereby said cathodefollower action of said electron discharge causes the cathode of saidelectron discharge device and said screen grid of said pentode to`remain at a substantially constant potential; means. to, apply aprogressively decreasing potential to said anode of said pentode, saidmeans includingacapacitance connected. to said anode, means for chargingsaid capacitance to a predetermined potential which is higher than saidAsubstantially constant potential', means to discharge said capacitancewhereby when the potential of said capacitance and said anode of saidpentode become lower than the substantially constant potential appliedto said screen grid of said pentode there is a surge of current to saidscreen grid; and an output termi-nal connected to saidY screen grid.

5. A circuit for producing a sharp pulse, comprising: a pentode havingan anode, a screen grid, a cathode, and a control grid; means to apply asubstantially constant potential to said screen grid, said meanscomprising an electron discharge device having an anode, a control grid,and a'cathode, a connection between said cathode of said electrondischarge device and saidV screen grid of said pentode `whereby saidscreen grid cathode impedance of said' pentode acts asa cathode load forsaid device causing it 'to Yact asY a cathode follower, a source ofsubstantially constant potential, a connection between said controlgridof said'electron discharge deviceand' said source whereby saidcathode follower action. of said electron discharge causes the cathodeofI said electron discharge device and said screen grid of said pentodeto remain at a, vsubstantially constant potential; means to apply aprogressively decreasing potentialv to said anode 'of said pentode, saidmeans including4 a sweep capactor connected' to saidanode, means forcharging said capacitor to a predetermined potential which is higherthan said substantially constant potential,- means to discharge saidcapacitor, and thus reduce the potentialV at` said anode lof saidpentode whereby when the potential' of said anode of said pentodebecomesI lower than the substantially constant potential applied to saidscreen, grid of said' pentode there is a surge of current to said screengrid; utilization means adapted to be energized, by said surge, saidmeans comprising a circuit connected to said screen grid, said circuitcomprising said electron discharge device and a resistance connectedtothe anode ther-coli;` an output terminal' connected to the anodeof'saidelctron discharge device.

6.l A circuit, for producing a. Shlp pulse, comprising: a pentode havingan anode, a screen grid a cathode, and a control grid; means to apply asubstantially constant potential to, said screen grid, saidV meanscomprising an electron discharge device having an anode, a control grid,and, a cathodepa connection between said cathode of said electrondischarge device and said screen grid of said pentode whereby saidscreen .grid cathode circuit of said pentode ycauses said electrondischarge device tol act asa cathodefollower, a source-of substantiallyconstant potential, a` connection between Vsaid control grid of saidelectron discharge device and said source, whereby said cathode4follower action of said electron discharge causes the. cathode of saidelectron discharge devlice and said screen grid of said pentode tovremain at a. substantially constant potential; means to apply a4progressively decreasing potential tov saidf anodeY of said pentode,`said means. including a sweep capacitor connected to said anode, meansfor charging said capacitor to a predetermined potential whichds higherthan said' substantially constant potential, means to discharge saidcapacitor, and thus reduce the potential at 'said lanode off saidpentode whereby when the potential of said anode of said pentode becomeslower than the substantially constant: pote applied to 'said'vscrecngrid Of Said; pentode there is a surge of current to said screengrid; utilization means adapted to be energized by said surge, saidmeans comprising a circuit connected to said screen grid, said circuitcomprising said electron discharge device and a resistance connected tothe anode thereof; an output terminal connected to the anode of saidelectron discharge device; and means, energized by the output signalproduced at said output terminal, for causing said pentode to becomenon-conductive whereby said capacitance may be charged, said meanscomprising a connection between said control grid of said pentode andsaid last-named means.

7. A circuit comprising a pentode (acting as a constant current device)having an anode, a screen grid, and a control grid; means applying asubstantially constant potential to said screen grid; a work circuitconnected to said screen grid; means causing the potential at said anodeto drop below the potential at said screen grid whereby saidsubstantially constant current is diverted from said 6 anode to saidscreen grid to form a surge of current Ithrough said Work circuit; andmeans causing said current surge through said work circuit to cut o saidpentode, said means comprising a connection between said work circuitand said control grid.

References Cited in the le of this patent UNITED STATES PATENTS1,464,533 Loewe Aug. 14, 1923 1,910,099 Farnham May 23, 1933 1,933,773Terman Nov. 7, 1933 2,231,377 Anderson Feb. 11, 1941 2,246,958 Strutt etal. lune 24, 1941 2,275,016 Koch Mar. 3, 1942 2,494,865 Fleming-Williamset al. Jan. 17, 1950 2,640,103 Clements May 26, 1953 2,644,886 HollandJuly 7, 1953

